In the case of manufacturing a multilayer printed wiring board by e.g. a build-up method, it is necessary to flatten the surface of a lower layer substrate in order to increase the wiring density. However, the circuit patterns of a printed wiring board may be manufactured by a subtractive method for removing unnecessary parts of copper foil via etching. As a result, the printed wiring boards are generally formed into an uneven configuration. The part representing the circuit pattern typically rises above the surrounding surface of the base material.
Therefore, in order to flatten a printed board in which the surface is formed in an uneven form as described above the following method has been proposed. The method comprises laminating a semi-cured resin sheet onto circuit patterns; pressing the resin sheet in a reduced pressure atmosphere so as to have the resin fill in the spaces between the circuit patterns, and curing the resin; and polishing the cured resin covering the circuit patterns; in order to obtain a smoothed substrate with exposed circuit patterns.
Heretofore, a laminating press has generally been utilized for manufacturing a multilayer substrate by pressing a laminated body. The laminated body is formed by laminating a prepreg and a metallic foil, etc., onto an uneven core substrate on which circuit patterns are formed. In the laminating press, which is intended for making a multilayered substrate (i.e. for laminating an insulation layer onto the circuit patterns), there has been a condition in which the pressing must be performed while adjusting the pressing pressure and the pressing amount (i.e., distance), etc., in order to make the insulating layer on the circuit patterns have a predetermined thickness. In the above described circumstances, the pressing condition may be so demanding that it is difficult to collectively press a plurality of sets of laminated bodies. More specifically, in the case where a plurality of sets of laminated bodies are arranged to be collectively pressed in order to form a number of individual laminated bodies with a predetermined thickness, various conditions such as the pressing pressure and the heat transfer rate in each laminated body need to be made uniform across the whole group of laminated bodies. To this end, smoothing plates must be arranged between respective laminated bodies. Accordingly, a configuration for performing collective pressing via the arranging of smoothing plates between respective laminated bodies has been generally adopted in the art of laminated pressing.
However, the above described method of performing collective pressing by arranging smoothing plates between respective laminated bodies has a problem in that the number of laminated bodies that can be received by a pressing machine with a fixed width is reduced by the thickness of the plurality of smoothing plates. As a result, the productivity level of the laminating press is lowered.
The present invention has been made in view of the above described circumstances. An object of the present invention is to provide a method for manufacturing a flat printed wiring board and with a relatively excellent level of productivity.